1. Field of the Invention
The present invention relates to the field of audio detectors and audio alarms, and is more particularly directed to a noise alarm used in a classroom to detect and react to noise exceeding a predetermined level and constitutes, in part, certain improvements relating to the invention specified in U.S. Pat. No. 4,346,374 issued to the present applicant on Aug. 24, 1982.
2. Description of the Prior Art
It is desirable for the instruction to maintain an acceptable classroom noise level during a given learning situation, so that both students and teacher can concentrate on the lesson at hand. Too often the teacher must repeat the shopworn phrase, "You're too noisy!" even when the class is highly motivated and well-behaved, since the combined whispers and comments of thirty or so exuberant youngsters can quickly build to an ear-splitting crescendo. To objectively and automatically maintain an acceptable classroom noise level, an electronic audio alarm is placed within the classroom to detect and react to any noise which exceeds a given sound level, as predetermined by the instructor. For example, the alarm is adjusted so that associated sounding means are actuated to automatically notify the students when classroom noise exceeds a "whisper" level.
To further reinforce the noise alarm, the device incorporates counting and display means which count and display in digital form the total number of times the alarm has been actuated in response to excessive classroom noise. Usually the instructor will use the resulting "count" to penalize the class for being noisy by translating the count displayed into one minute per count, so the students are dismissed later than normal or receive less recess or P.E. time. Since the alarm device functions independently of the teacher, it can be used to maintain an acceptable classroom noise level when the teacher is not physically present in the classroom, as, for example, during a recess or lunch period.
The classroom noise alarm of U.S. Pat. No. 4,346,374 also incorporates a time delay mechanism to make the alarm more tolerant of occasional noise by inhibiting the sounding means and count display unless noise occurs frequently and within a predetermined time frame. The above device exhibits a minor disadvantage, however, in that the alarm can be enabled or actuated by short duration noise, such as that of a door slam, a book falling to the floor, or a cough. The alarm can also be triggered by loud, continuous noise, such as that of a classroom recess bell.
In attempts to obviate these disadvantages, other educational noise alarm devices have been invented. U.S. Pat. No. 4,416,155 incorporates a capacitor-voltage comparator circuit in which classroom noise exceeding a preset level causes a capacitor to charge to a threshold voltage level. When the voltage threshold is reached, as determined by an associated comparator, an alarm is actuated. Sharp, isolated noises are not long enough in duration to charge the capacitor to a nominal threshold voltage and will, thus, be ignored. Another alarm device, U.S. Pat. No. 4,481,504, incorporates an oscillator circuit which repeatedly enables the alarm device for a brief time every 2.5 seconds in a first selective mode and every 6-7 seconds in a second mode. An associated alarm sounds if classroom noise, in excess of a preselected level, occurs within a brief time frame either in the first or second mode. A third alarm device, U.S. Pat. No. 4,529,973, includes a large filter capacitor in the audio signal rectifier circuit, which causes the alarm to ignore short, non-repetitive noises. None of the above noise alarm devices addresses the "false alarm" problem caused by long duration noise, such as that of a recess bell or even a pencil sharpener.
A major disadvantage of U.S. Pat. No. 4,346,374, other than being unable to ignore short and long duration noise, is that any of several controls on the device are easily accessible to students and can be surreptitiously manipulated to defeat the sounding means, count display, or both. Tampering can easily be accomplished when the instructor is not physically present in the classroom, and possibly even when he is present. It is, therefore, a general object of the present invention to provide a tamperproof classroom noise alarm.